Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 020640
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
840 PM HST FRI AUG 1 2014

.SYNOPSIS...
AN AREA OF DEEP TROPICAL MOISTURE WILL CONTINUE TO MOVE WESTWARD
ACROSS THE STATE TONIGHT AND SATURDAY. NUMEROUS SHOWERS WILL AFFECT
WINDWARD AREAS...WITH SOME SHOWERS SPILLING OVER INTO LEEWARD
SECTIONS AS WELL. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE TONIGHT
AND SATURDAY. DRIER AND MORE STABLE TRADE WIND WEATHER IS
EXPECTED SUNDAY THROUGH WEDNESDAY. ANOTHER BOUT OF WET WEATHER IS
POSSIBLE LATE NEXT WEEK.

&&

.DISCUSSION...
A WET EVENING IS IN PROGRESS ACROSS THE BIG ISLAND OF HAWAII...
WITH RADAR LOOPS SHOWING WIDESPREAD SHOWER ACTIVITY ACROSS THAT
AREA. A FLOOD ADVISORY WAS RECENTLY ISSUED FOR PARTS OF THE
HAMAKUA COAST. SHOWERS ARE ALSO INCREASING ACROSS THE ALENUIHAHA
CHANNEL AND EAST MAUI. FURTHER WEST...LIGHTER SHOWERS ARE
MOVING OVER WINDWARD OAHU...WHILE ACTIVITY REMAINS SPARSE OVER
KAUAI. THERE WERE A COUPLE OF THUNDERSTORMS DURING THE LATE
AFTERNOON ACROSS THE BIG ISLAND INTERIOR...BUT THESE DIED DOWN
BEFORE SUNSET.

MIMIC-TPW SATELLITE IMAGERY CLEARLY SHOWS THE SURGE OF DEEP
TROPICAL MOISTURE MOVING WESTWARD ACROSS THE STATE...WITH
ESTIMATED PWATS OVER 2 INCHES EXTENDING FROM JUST NORTH OF THE BIG
ISLAND AND MAUI SOUTHWARD INTO THE DEEP TROPICS. THE 00Z SOUNDINGS
DEPICTED A SHARP MOISTURE GRADIENT ACROSS THE STATE...WITH A
MEASURED PWAT OF 2.21 INCHES AT HILO AND AND 1.36 INCHES AT LIHUE.
THIS PWAT VALUE AT HILO IS MORE THAN 3 STANDARD DEVIATIONS ABOVE
NORMAL. HILO ALSO SHOWED A MOIST ADIABATIC PROFILE WITH NO
INVERSION PRESENT...WHILE AN INVERSION BASED NEAR 7000 FEET
PERSISTED AT LIHUE. AT THE SURFACE...MODERATE TRADES CONTINUE
ACROSS THE STATE...BETWEEN HIGH PRESSURE TO OUR NORTHEAST AND THE
REMNANT LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE TO OUR SOUTH.
ALOFT...WATER VAPOR IMAGERY DEPICTS A WEAK UPPER LEVEL TROUGH
SLIDING EASTWARD SEVERAL HUNDRED MILES NORTH OF THE STATE...WITH A
MID LEVEL RIDGE EXTENDING WEST ACROSS THE BIG ISLAND.

THROUGH THE OVERNIGHT...EXPECT INCREASING SHOWERS AND LOCALLY
HEAVY RAINFALL TO CONTINUE SPREADING WESTWARD ACROSS THE STATE.
WITH ONLY MODEST INSTABILITY IN PLACE (500 MB TEMPS OF -6C AND
NEARLY MOIST ADIABATIC PROFILES) AND LITTLE UPPER SUPPORT
EVIDENT...WOULD EXPECT THIS TO BE MAINLY AN OROGRAPHICALLY
DRIVEN EVENT WITH THE HEAVIEST RAINS FAVORING MAINLY WINDWARD
AREAS. HOWEVER...ISOLATED HEAVY DOWNPOURS WILL BE POSSIBLE
OVER LEEWARD AREAS AS WELL. POTENTIAL FOR THUNDERSTORMS SHOULD
REMAIN LOW...BUT AN ISOLATED STORM IS NOT TOTALLY OUT OF THE
QUESTION. THE EXISTING FORECAST APPEARS TO HAVE A GOOD HANDLE ON
THE EXPECTED EVOLUTION...AND NO UPDATES ARE CURRENTLY PLANNED FOR
THIS EVENING.

FREQUENT WINDWARD SHOWERS AND LOCALLY HEAVY RAINS WILL CONTINUE
ACROSS THE STATE INTO SATURDAY MORNING...WITH THE FOCUS OF
ACTIVITY SHIFTING FURTHER WESTWARD ACROSS THE SMALLER ISLANDS
DURING THE DAY. RAIN CHANCES SHOULD DECREASE SOMEWHAT BY
AFTERNOON...WITH THE HEAVY RAIN THREAT DIMINISHING AS THE AREA
OF HIGHEST TROPICAL MOISTURE PASSES WEST OF KAUAI.

SATURDAY NIGHT AND SUNDAY SHOULD SEE A DRYING TREND WITH
DECREASING DEWPOINTS AS A MUCH DRIER AIRMASS MOVES IN FROM
THE EAST. A DRY/STABLE TRADE WIND PATTERN IS EXPECTED FOR
MONDAY THROUGH WEDNESDAY...WITH RIDGING ALOFT AND BELOW NORMAL
PWATS KEEPING SHOWER ACTIVITY SOMEWHAT SPARSE AND MAINLY
CONFINED TO WINDWARD AREAS.

LOOKING FURTHER AHEAD TOWARD THURSDAY AND FRIDAY OF NEXT WEEK...
FOR THE PAST SEVERAL CYCLES NOW GLOBAL MODELS HAVE CONSISTENTLY
BROUGHT YET ANOTHER SURGE OF DEEP TROPICAL MOISTURE TOWARD THE
STATE FROM THE EAST. THIS MOISTURE IS ASSOCIATED WITH THE MODEL
DEPICTION OF CURRENT EAST PACIFIC TROPICAL STORM ISELLE. IT
REMAINS HIGHLY UNCERTAIN AT THIS POINT WHETHER ISELLE OR ITS
REMNANTS WILL EVENTUALLY REACH THE VICINITY OF HAWAII...BUT THERE
IS THE POTENTIAL FOR ANOTHER BOUT OF WET WEATHER TOWARD THE END OF
NEXT WEEK. STAY TUNED FOR FORECAST UPDATES DURING THE NEXT SEVERAL
DAYS.

&&

.AVIATION...
TROPICAL MOISTURE CONTINUES TO SPREAD WESTWARD ACROSS THE MAIN
HAWAIIAN ISLANDS THIS EVENING. SO FAR...THIS MOIST AIR MASS HAS
PRODUCED ABUNDANT LOW CLOUDS AND SHOWERS WITH LOWER CEILINGS AND
REDUCED VISIBILITIES OVER THE WINDWARD SECTIONS AND HIGHER TERRAIN
OF THE BIG ISLAND...MAUI AND MOLOKAI. THERE WERE ALSO THUNDERSTORMS
OVER THE BIG ISLAND SUMMITS RECENTLY...BUT THESE COLLAPSED BEFORE
SUNSET. AIRMET SIERRA REMAINS IN EFFECT FOR MOUNTAIN OBSCURATION ON
THE ISLANDS. THIS AIRMET WILL LIKELY REMAIN IN EFFECT FOR THESE
LOCATIONS THROUGH TONIGHT.

WEST OF MOLOKAI...VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS MOST
LEEWARD SECTIONS OF OAHU AND KAUAI. HOWEVER...MVFR CONDITIONS WILL
LIKELY AFFECT WINDWARD FACING SLOPES AND THE HIGHER TERRAIN ON BOTH
OF THESE ISLANDS TONIGHT. IN FACT...MOUNTAIN OBSCURATION MAY
EVENTUALLY DEVELOP ON OAHU AND KAUAI...SO AIRMET SIERRA MAY BE
REQUIRED FOR ADDITIONAL PARTS OF THE STATE LATER TONIGHT OR EARLY
SATURDAY MORNING.

AS A RESULT OF THE MODERATE TO LOCALLY BREEZY LOW-LEVEL TRADE WIND
FLOW...AIRMET TANGO REMAINS IN EFFECT FOR LOW-LEVEL TURBULENCE BELOW
8 KFT IMMEDIATELY SOUTH THROUGH WEST OF THE HIGHER TERRAIN ON ALL
ISLANDS. BASED ON THE LATEST GUIDANCE...THIS AIRMET WILL LIKELY
REMAIN IN EFFECT THROUGH SATURDAY.

&&

.MARINE...
A 2006Z ASCAT PASS CLIPPED THE FAR WESTERN EDGE OF THE HAWAIIAN
COASTAL WATERS...AND FOUND WINDS ONLY NEAR 15 KNOTS IN THE WATERS
AROUND KAUAI. THERE IS A MODERATE PRESSURE GRADIENT IN PLACE
ACROSS THE AREA BETWEEN HIGH PRESSURE TO THE NORTH AND THE REMNANT
LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE TO THE SOUTH...AND
WILL MAINTAIN THE EXISTING SMALL CRAFT ADVISORY FOR THE TYPICALLY
WINDY WATERS AROUND MAUI COUNTY AND THE BIG ISLAND. HOPEFULLY THE
OVERNIGHT ASCAT PASS WILL PROVIDE ADDITIONAL WIND DATA ACROSS
THE ADVISORY AREA.

INCREASING SSW SWELL IS EXPECTED TONIGHT AND SATURDAY WITH SURF
APPROACHING ADVISORY LEVELS ON SOUTH FACING SHORES. THIS SURF
EVENT WILL SLOWLY DECREASE SUNDAY THROUGH MONDAY. SURF WILL SEE A
SLIGHT BUMP ON WEST FACING SHORES AS WELL DUE TO THE SSW
DIRECTION. LOW END SOUTH SWELL WILL MAINTAIN BACKGROUND SURF ALONG
SOUTH SHORES TUESDAY AND WEDNESDAY. OTHERWISE...PREVAILING TRADE
WINDS WILL CONTINUE TO PRODUCE SHORT PERIOD SWELL AND CHOPPY NEAR
AVERAGE SURF ALONG EAST FACING SHORES THROUGH THE NEXT SEVERAL
DAYS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...HOUSTON






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